In a large stock pot or Dutch oven over medium heat, add butter. When butter is melted, add onions and celery. Mix and cook for a few minutes until soft.
Add chicken stock and spices and stir well. Add diced potatoes and bring the mixture to a boil with the pot covered partially. Cook until potatoes are tender.
When adding the flour to create a thick paste, don’t dump it in one place. Dust it evenly over the vegetable mixture to help prevent lumps and guarantee a smooth consistency.